The hydrolysis of xylo-oligosaccharides catalyzed by β-xylosidase plays an important role in the degradation of lignocellulose. However, the enzyme is easily inhibited by its catalytic product xylose, which severely limits its application. Based on molecular docking, this paper studied the xylose affinity of Aspergillus niger β-xylosidase An-xyl, which was significantly differentially expressed in the fermentation medium of tea stalks, through cloning, expression and characterization. The synergistic degradation effect of this enzyme and cellulase on lignocellulose in tea stems was investigated. Molecular docking showed that the affinity of An-xyl to xylose was lower than that of Aspergillus oryzae β-xylosidase with poor xylose tolerance. The K_i value of xylose inhibition constant of recombinant-expressed An-xyl was 433.2 mmol/L, higher than that of most β-xylosidases of the GH3 family. The K_m and V_max towards pNPX were 3.6 mmol/L and 10 000 μmol/(min·mL), respectively. The optimum temperature of An-xyl was 65 ℃, the optimum pH was 4.0, 61% of the An-xyl activity could be retained upon treatment at 65 ℃ for 300 min, and 80% of the An-xyl activity could be retained upon treatment at pH 2.0-8.0 for 24 h. The hydrolysis of tea stem by An-xyl and cellulase produced 19.3% and 38.6% higher reducing sugar content at 2 h and 4 h, respectively, than that of using cellulase alone. This study showed that the An-xyl mined from differential expression exhibited high xylose tolerance and higher catalytic activity and stability, and could hydrolyze tea stem lignocellulose synergistically, which enriched the resource of β-xylosidase with high xylose tolerance, thus may facilitate the advanced experimental research and its application.
Aspergillus niger/genetics* ; Xylose/metabolism* ; Molecular Docking Simulation ; Xylosidases/genetics* ; Cellulases ; Tea ; Hydrogen-Ion Concentration ; Substrate Specificity

A xylosidase gene, labeled as BH1068 in genome of Bacillus halodurans C-125, was successfully cloned and overexpressed in Escherichia coli JM109. The purified enzyme was thoroughly characterized and its xylosidase function was unambiguously confirmed. It has maximum activities in neutral condition and is stable over a wide range of pH (4.5-9.0). The enzyme has a broad temperature optimal (35 degrees C-45 degrees C) and is quite stable at temperature up to 45 degrees C. The unique pH and temperature profiles of the enzyme should allow a wide range of xylanolytic operational conditions. With high specific activity of 174 mU/mg protein for its artificial substrate (p-nitrophenyl-beta-xylose) and low xylose inhibition (inhibitor constant Ki = 300 mmol/L), this enzyme is among the most active and high tolerant bacterial xylosidase to xylose inhibition. Its high synergy with commercial xylanase has been demonstrated with beechwood xylan hydrolysis, achieving a hydrolysis yield of 40%. Its neutral pH optimal and high tolerance to product inhibition complements well with its fungal counterparts that are only optimal at acidic pH and susceptible to xylose inhibition. In conclusion, this enzyme has high potential in the saccharification of xylan and xylan-containing polysaccharides.
Amino Acid Sequence ; Bacillus ; classification ; enzymology ; genetics ; Cloning, Molecular ; Escherichia coli ; genetics ; metabolism ; Hydrolysis ; Molecular Sequence Data ; Recombinant Proteins ; genetics ; metabolism ; Substrate Specificity ; Xylose ; metabolism ; Xylosidases ; genetics ; metabolism

A beta-D-xylosidase from Leifsonia shinshuensis DICP 16 was purified to apparent homogeneity using a combination of ammonium sulfate precipitation, DE 52 anion-exchange, Q-Sepharose Fast Flow anion-exchange, Toyopearl Butyl 650C hydrophobic-interaction and Sephacryl S-300 HR gel-permeation chromatography. The purified xylosidase consisted of two same subunits and had the relative molecular weight of 180 kD as determined by SDS-PAGE and gel-permeation chromatography. The maximal beta-D-xylosidase activity occurred at 55 degrees C and pH 7.0. It was stable at 45 degrees C and retained its original activity for 60 min. The stability declined rapidly when the temperature rose above 55 degrees C. The xylosidase was stable in the pH range from 6.0 to 11.0 for 20 h. At pH 7.0 and 45 degrees C the Km for p-nitrophenyl-beta-D-xylopyranoside (pNPX) was 1.04 mmol/L and the Vmx was 0.095 mmol nitrophenol/min/mg xylosidase. The enzyme was inhibited strongly by Fe2+ and Cu2+. It exhibited low levels of activity against other artificial substrates, compared to its activity against pNPX. When different natural xylosides were used as the substrates, the xylosidase showed distinct hydrolysis ability. It could hydrolyze 20-C, beta-(1-->6)-xyloside of ginsenoside Rb3 (G-Rb3) into ginsenoside Rd, but did not hydrolyze the other beta-D-glucosidic bonds of G-Rb3. Additionally, the xylosidase could not hydrolyze C-7 xylosyl-bearing taxanes.
Actinomycetales ; classification ; enzymology ; Amino Acid Sequence ; Culture Media ; Hydrogen-Ion Concentration ; Molecular Sequence Data ; Sequence Analysis, Protein ; Temperature ; Xylosidases ; chemistry ; genetics ; isolation & purification

Xylanase can hydrolyze xylans into xylooligosaccharides and D-xylose, and has great prospect for applications in feed industry, paper and pulp industry, food industry and environment science. The study of xylanase had been started in 1960's. With the development and application of the new technologies, such as molecular biology, structural biology and protein engineering, many progresses have been made in the research of structures and functions of xylanase. This paper reviews the research progress and trend in the structure correlating with the important properties of xylanase. Analyses of three-dimensional structures and properties of mutants have revealed that glutamine and aspartic acid residues are involved in the catalytic mechanism. The thermostability of xylanase correlated with many factors, such as disulfide bridges, salt bridges, aromatic interactions, cotent of arginine and proline, and some multidomain xylanase have thermostability domains in N or C terminal. But no single mechanism is responsible for the remarkable stability of xylanase. The isoelectic points and reaction pH of xylanase are influenced by hydrophobicity and content of electric charges. Many researches had demonstrated that aromatic amino acid, histidine, and tryptophan play an important role in improving enzyme-substrate affinity. The researches of structures and functions of xylanase are of great significance in understanding the catalytic mechanism and directing the improvement of xylanase properties to meet the application requirement.
Catalysis ; Endo-1,4-beta Xylanases ; chemistry ; metabolism ; Enzyme Stability ; Protein Engineering ; Substrate Specificity

OBJECTIVETo study the optimal medium composition for xylanase production by Aspergillus niger XY-1 in solid-state fermentation (SSF).

METHODSStatistical methodology including the Plackett-Burman design (PBD) and the central composite design (CCD) was employed to investigate the individual crucial component of the medium that significantly affected the enzyme yield.

RESULTSFirstly, NaNO(3), yeast extract, urea, Na(2)CO(3), MgSO(4), peptone and (NH(4))(2)SO(4) were screened as the significant factors positively affecting the xylanase production by PBD. Secondly, by valuating the nitrogen sources effect, urea was proved to be the most effective and economic nitrogen source for xylanase production and used for further optimization. Finally, the CCD and response surface methodology (RSM) were applied to determine the optimal concentration of each significant variable, which included urea, Na(2)CO(3) and MgSO(4). Subsequently a second-order polynomial was determined by multiple regression analysis. The optimum values of the critical components for maximum xylanase production were obtained as follows: x(1) (urea)=0.163 (41.63 g/L), x(2) (Na(2)CO(3))=-1.68 (2.64 g/L), x(3) (MgSO(4))=1.338 (10.68 g/L) and the predicted xylanase value was 14374.6 U/g dry substrate. Using the optimized condition, xylanase production by Aspergillus niger XY-1 after 48 h fermentation reached 14637 U/g dry substrate with wheat bran in the shake flask.

CONCLUSIONBy using PBD and CCD, we obtained the optimal composition for xylanase production by Aspergillus niger XY-1 in SSF, and the results of no additional expensive medium and shortened fermentation time for higher xylanase production show the potential for industrial utilization.

A model describing the solubilization of arabinoxylans and degradation by endo-xylanase random attacking during mashing was developed. The model was expected to predict the arabinoxylans concentration in wort at the settings of different initial value and mashing parameters for diminishing the negative effects of arabinoxylans on brewing. Results showed that the modeling errors range for the final concentration of arabinoxylans in wort was -9.5% to +13.6%. The model prediction accuracy for industrial scale mashing process was lower than that in laboratory scale. The errors were given 16.8% and 17.9%, respectively. The simulation results showed that arabinoxylans concentration was increased with the increase of mashing-in temperature, but it was decreased with prolonging the mashing-in time. The effect of initial arabinoxylans in malt on arabinoxylans concentration in wort was more remarkable than that of endo-xylanase activity in grist.
Endo-1,4-beta Xylanases ; metabolism ; Enzyme Activation ; Fermentation ; Models, Chemical ; Solubility ; Xylans ; metabolism

Besides the catalytic domain, some xylanases contained a non-catalytic domain which is named as carbohydrate binding module (CBM). CBM can be used to improve their binding-ability to insoluble substrates. We illustrated the importance of CBM by reviewing the source of CBMs, type of families, features of binding to insoluble substrates, specific amino acids involved in substrate-binding, linker peptides connecting the catalytic domain, and the effect of CBMs on xylanase thermostability. CBM is important for xylanase to break down complicate carbohydrates. Perspectives on engineering xylanase activity according to the characteristics of CBMs were given.
Binding Sites ; Carbohydrate Metabolism ; Catalysis ; Endo-1,4-beta Xylanases ; metabolism ; Multienzyme Complexes ; chemistry ; Substrate Specificity

Xylanase is the key enzyme to degrade xylan that is a major component of hemicellulose. The enzyme has potential industrial applications in the food, feed, paper and flax degumming industries. The use of xylanases becomes more and more important in the paper industry for bleaching purposes. Xylanases used in the pulp bleaching process should be stable and active at high temperature and alkaline pH. Thermophilic and alkalophilic xylanases could be obtained by screening the wild type xylanases or engineering the mesophilic and neutral enzymes. In this paper, we reviewed recent progress of screening of the thermophilic and alkalophilic xylanases, molecular mechanism of thermal and alkaline adaptation and molecular engineering. Future research prospective was also discussed.
Endo-1,4-beta Xylanases ; chemistry ; Enzyme Stability ; Hot Temperature ; Hydrogen-Ion Concentration ; Paper ; Protein Engineering

Thermophilic and alkalophilic xylanases have great potential in the pulp bleaching industry. In order to improve the thermal stability of an alkaline family 11 xylanase Xyn11A-LC, aromatic residues were introduced into the N-terminus of the enzyme by rational design. The mutant increased the optimum temperature by 5 degrees C. The wild type had a half-time of 22 min at 65 degrees C and pH 8.0 (Tris-HCl buffer). Under the same condition, the mutant had the half-time of 106 min. CD spectroscopy revealed that the melting temperature (T(m)) values of the wild type and mutant were 55.3 degrees C and 67.9 degrees C, respectively. These results showed that the introduction of aromatic residues could enhance the thermal stability of Xyn11A-LC.
Endo-1,4-beta Xylanases ; chemistry ; Enzyme Stability ; Hydrogen-Ion Concentration ; Protein Engineering ; Temperature

The endo-1,4-xylanase gene from Bacillus pumilus HB030 was cloned into the Pichia pastoris expression vector, pPIC9k, the recombinant plasmid was named pHBM220. The digested recombinant plasmid pHBM220 was transformed into Pichia pastoris KM71, GS115, SMD1168, respectively. The recombinant Pichia pastoris KM71 (pHBM220), GS115 (pHBM220), SMD1168 (pHBM220) secreted functional endo-1,4-xylanase, and the enzymatic activities reached 10.80IU/mL, 11.63IU/mL, 9.68IU/mL, respectively. The temperature and pH optimum for the recombinant xylanase were 60 degrees C and pH5.5, respectively.
Bacillus ; enzymology ; genetics ; Electrophoresis, Polyacrylamide Gel ; Endo-1,4-beta Xylanases ; genetics ; metabolism ; Hydrogen-Ion Concentration ; Pichia ; genetics ; metabolism ; Temperature